<!DOCTYPE html>
<html>
    <head>
        <meta charset='utf-8' />
        <style>     
            h1,h2,#aaa{color:red;} /*组合选择符*/
        </style>
    </head>
    <body>
        <h1>我是H1</h1>
        <h2>我是H2</h2>
        <h3 id='aaa'>我是H3</h3>
    </body>
</html>